Most of the manuscript's differentiae appear in two or three slightly different forms, indicated in the index by minuscule letters following the main differentia number. Much of the second ("b") layer of differentiae has been added by a second hand which obscured the neumatic differentiae (in the original sections of the manuscript) with differentiae notated on small marginal staves (ff. 162v-164r, 167v-173v, 176r-178r, 179r-181r, 183v-186v, 208r-228r). The differentiae in the sections added to the manuscript (usually included in the main body of each page rather than in the margin) also conform most often to the second layer, but occasionally are entirely different.

Several unusual Offices are found in both the original and added sections of the manuscript. Some have been edited in Analecta hymnica, such as Lambert (26: 230-33), Catherine of Alexandria (26: 212-15), the Visitation (attributed to Cardinal Adam Easton, 24: 89-92), and Adrian (25: 18-21). The Office for Servatius (Bishop of Tongres) in Utrecht 406 is a more complete version of the one edited in Analecta hymnica vol. 5, pp. 214-16. Sections of the added Office for Mary Magdalene (146v), not found in Analecta hymnica, also occur in several other manuscripts indexed by CANTUS.

Another Office not in Analecta hymnica, for Cornelius and Cyprian, may also be found in Cambrai 38. The Office for Corpus Christi (attributed to Thomas Aquinas) was not edited in Analecta hymnica but occurs in other CANTUS manuscripts. The Translation of Lebuin (or Liafwine, the English missionary to the Saxons of the Netherlands), the Translation of Martin, Remigius (Bishop of Rheims), Gereon and Companions (martyrs, supposedly at Cologne), Willibrord (Bishop of Utrecht), and the Transfiguration are not in Analecta hymnica , Andrew Hughes's Late Medieval Liturgical Offices, or in other CANTUS files. The literary texts for the Offices for Lebuin and Martin are drawn from sermons of Ratbod, a former bishop of Utrecht.

In addition to the six sequences notated on ff. 1-4, Utrecht 406 includes several other Mass chants, either complete or in incipit, most on added folios. The introits for the midnight and dawn Masses of Christmas are indicated by incipit ("Dominus dixit," 23v; and "Lux fulgebit," 24r). The alleluia with verse, sequence, and offertory for Corpus Christi have been included on ff. 139-140. For Immaculate Conception (151r), the introit, offertory, and communion have been notated in full, and the gradual and alleluia in incipit.

Manuscripts from this region of Europe have been described as transitional sources, often having both eastern and western characteristics. For example, some antiphon texts in Utrecht 406 are included twice, with different melodies: "Ecce Maria genuit nobis" (cao2523), 35v and 36v; "Stephanus servus dei quem" (cao5027), 37r and 37v; "Egressus Jesus secessit" (cao2620), both on 74v; "Surrexit dominus de sepulcro" (cao5079), 101r and 101v; "Iterum autem videbo vos" (cao3465), both on 106r; and "Attendite a falsis prophetis" (cao1511), both on 224r. Some responsories in Utrecht 406 have two different verses--on a feast and its octave, for example--sometimes with both a standard and non-standard verse formula: "Centum quadraginta quattuor" (cao6273), 33r and 38r; "In medio ecclesiae aperuit os" (cao6913), 30r and 38r; and "Quem vidistis pastores dicite" (cao7470), 22v and 36r.

We would like to acknowledge the help of the offerings of the Thesaurus Musicarum Latinarum, which made the identification of the manuscript's music-theoretical excerpts (ff. 228v-233v) possible in less than one hour. The TML can be accessed at http://www.music.indiana.edu/tml/. More detailed information about this section of the manuscript may be found in one of the RISM volumes covering music-theoretical sources (see below).

All chants not found in CAO are assigned arbitrary numbers prefixed by "utr".

de Loos, Ike. "The Transmission of the responsoria prolixa according to the Manuscripts of St. Mary's Church Utrecht." Tijdschrift van de Koninklijke Vereniging voor Nederlandse Muziek Geschiedenis 41 (1999): pp. 5-31.